US7175825B2 - Method of producing titania solution - Google Patents

Method of producing titania solution Download PDF

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US7175825B2
US7175825B2 US10/863,722 US86372204A US7175825B2 US 7175825 B2 US7175825 B2 US 7175825B2 US 86372204 A US86372204 A US 86372204A US 7175825 B2 US7175825 B2 US 7175825B2
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titania
solution
amorphous
anatase
particles
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US20050123471A1 (en
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Katsuyuki Nakano
Eiko Higashi
Takeshi Hayakawa
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Sundecor Co Ltd
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Sundecor Co Ltd
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Priority claimed from JP2004100337A external-priority patent/JP3641269B1/ja
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • C01G23/047—Titanium dioxide
    • C01G23/053—Producing by wet processes, e.g. hydrolysing titanium salts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/36—Compounds of titanium
    • C09C1/3607—Titanium dioxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram

Definitions

  • the present invention relates to a method of producing a titania solution containing non-crystalline titania and/or crystalline titania, which is, for example, used as a material of a coating film that exhibits photocatalytic activity.
  • Titania i.e. titanium oxide (TiO 2 )
  • TiO 2 titanium oxide
  • the titania coating film on the surface of the base material there has been used, for example, a method of applying a solution containing non-crystalline titania onto the surface of the base material, drying it, and then calcining it, or a method of applying a solution containing crystalline titania onto the surface of the base material, and then heating to dry it at a low temperature.
  • non-crystalline titania there is known, for example, such a solution that is obtained by dispersing fine particles of amorphous titania having a property of no existence of particle boundary into aqueous hydrogen peroxide.
  • the solution containing crystalline titania there is known, for example, such a solution that is obtained by dispersing fine particles of anatase titania into water. Examples of conventional methods of producing these solutions will be briefly described hereinbelow.
  • Titania is produced by mixing titanium tetraisopropoxide (TIP) and isopropanol (IPA) together at a predetermined mole ratio and agitating the mixture, then adding a predetermined amount of a liquid mixture of IPA and water into the mixture and agitating it. Then, the produced titania is separated from the mother liquid and then is subjected to airing to be dried, thereby obtaining powder of titania.
  • TIP titanium tetraisopropoxide
  • IPA isopropanol
  • the obtained powder is dissolved in aqueous hydrogen peroxide to produce a titania gel (a gel of titania), then aqueous hydrogen peroxide is further added as a dispersing agent to transform the titania gel to a titania sol (a sol of titania), thereby obtaining the titania solution containing fine particles of amorphous titania (e.g. see Patent Literature 1).
  • the solution containing amorphous titania is applied in the form of a thin film onto the surface of a base material such as ceramics or metal and dried, then calcined at a predetermined temperature such as at 500° C. to transform amorphous titania to anatase titania, thereby forming a titania coating film that exhibits photocatalytic activity, on the surface of the base material (e.g. see Patent Literature 2).
  • the solution containing anatase titania i.e. crystalline titania
  • a solution in which titanium hydroxide is dispersed as a material.
  • ammonia and sodium hydroxide are added into an aqueous solution of inorganic titanium compound such as titanium chloride or titanium sulfate to produce a titanium hydroxide gel.
  • aqueous hydrogen peroxide is added to thereby obtain a titanic acid solution. Non-reacted hydrogen peroxide is decomposed on standing.
  • titania may be aggregated in the solution so that a high dispersion state of titania can not be maintained.
  • the solution containing amorphous titania since amorphous titania is dispersed in aqueous hydrogen peroxide as described above, the solution has a strong acidity with a pH of, for example, about 1. With such a strong acidity, amorphous titania may be subjected to condensation polymerization so as to be gelled or aggregated.
  • titania may be gelled or lumped.
  • the solution containing anatase titania particles of titania may be mutually attracted to be aggregated.
  • titania since titania is dispersed in aqueous hydrogen peroxide in the preparation process of the titania solution, if the heat treatment for crystallization is carried out in the state where hydrogen peroxide remains, titania before crystallization may be gelled or aggregated particularly in the initial stage of the heat treatment.
  • the solution containing amorphous titania shows the acidity with the pH of, for example, about 1, selection of base materials applicable with the coating is limited. Particularly, if the metal base material is selected and applied with the titania solution, the surface thereof may be corroded. Further, since amorphous titania itself can not exhibit photocatalytic activity, when amorphous titania is used as the material of the coating film, calcination is required after the application of the titania solution onto the surface of the base material to thereby transform amorphous titania to anatase titania in order to obtain photocatalytic activity.
  • the present invention has been made under these circumstances and has an object to solve the problem about the stability of the titania solution as a product, or the problem upon using aqueous hydrogen peroxide as a dispersing agent in the production process, and to provide a method of producing a titania solution in which a dispersion state of particles of titania is stable, by suppressing gelling or aggregation of titania.
  • a method of producing a titania solution comprising the steps of dissolving titania in a first acid solution to produce a gel of amorphous titania; mixing the gel of amorphous titania and a second acid solution together to transform the gel of amorphous titania to a sol of amorphous titania; and supplying an alkali solution to the solution containing the sol of amorphous titania to adjust a pH of the solution to 2 to 10.
  • the step of producing the gel of amorphous titania may be a step of dissolving the titania while controlling a temperature of the first acid solution at 20° C. or below.
  • a method of producing a titania solution comprising the steps of mixing titania and an acid solution together, and dissolving the titania while controlling a temperature of the acid solution at 20° C. or below, to thereby produce a gel of amorphous titania; and mixing the gel of amorphous titania and an acid solution together to transform the gel of amorphous titania to a sol of amorphous titania.
  • the method may further comprise a step of heating the solution containing the sol of amorphous titania at a predetermined temperature for a predetermined time to crystallize the amorphous titania to thereby produce anatase titania.
  • This step may comprise a step of mixing particles of amorphous titania and water together, a step of applying ultrasonic waves to this mixture, and a step of heating the mixture applied with the ultrasonic waves, at a predetermined temperature to produce particles of anatase titania, and mix together the particles of anatase titania and the solution containing the sol of amorphous titania, and then heat the solution to produce anatase titania.
  • the anatase titania may contain anatase-rutile titania.
  • the titania solution may be a material of a coating film formed as a thin film on the surface of a base material and, in this case, the titania solution may contain silica.
  • a method of producing a titania solution comprising the steps of mixing together titanium tetraalkoxide, alcohol, and water that is excessive in amount relative to the titanium tetraalkoxide, to produce anatase titania and amorphous titania; and dissolving the anatase titania and the amorphous titania in an acid solution to obtain a dispersed liquid in which the anatase titania and the amorphous titania are dispersed.
  • a mixing mole ratio of the titanium tetraalkoxide relative to the water may be, for example, 1/10 ⁇ 80.
  • the titanium tetraalkoxide may be titanium tetraisopropoxide (TIP), and the alcohol may be isopropanol (IPA).
  • TIP titanium tetraisopropoxide
  • IPA isopropanol
  • the dispersed liquid may be heated at a predetermined temperature to produce anatase-rutile titania.
  • the dispersed liquid may contain the alcohol.
  • the dispersed liquid may be a material of a coating film formed as a thin film on the surface of a base material. In this case, the dispersed liquid may contain silica.
  • a production ratio between the anatase titania and the amorphous titania may be changed by changing a mixing mole ratio of the water relative to the titanium tetraalkoxide.
  • the step of dissolving the anatase titania and the amorphous titania in the acid solution may be carried out while controlling a temperature of the acid solution at 20° C. or below.
  • the method may further comprise a step of supplying an alkali solution to the dispersed liquid to adjust a pH of the dispersed liquid to 2 to 10.
  • the titania solution producing method of the present invention by adjusting the pH of the titania solution containing amorphous titania to 2 to 10 using the alkali solution, gelling or aggregation of titania can be suppressed even if the solution is, for example, left to stand at normal temperature for a long time. That is, it is possible to obtain the titania solution that can maintain the state where fine particles of titania are highly dispersed in the solution, over a long term. Further, if the solution is, for example, used as the material of the coating film, since it is possible to adjust the pH of the solution depending on a base material by adjusting the amount of the alkali solution, the base material is rarely deteriorated.
  • anatase titania being crystalline titania and amorphous titania being non-crystalline titania
  • amorphous titania is interposed among the particles of anatase titania to suppress aggregation of the particles of anatase titania. Therefore, even if the titania dispersed liquid is left to stand over a long term, the state where the particles of anatase titania are highly dispersed in the solution can be maintained.
  • anatase titania can be directly produced by hydrolysis of titanium tetraalkoxide, and therefore, the titania solution containing anatase titania can be easily produced without requiring, for example, a high temperature heat treatment.
  • FIG. 1 is an explanatory diagram showing processes of producing a solution containing amorphous titania, according to a titania solution producing method of the present invention
  • FIG. 2 is an explanatory diagram showing processes of producing a solution containing anatase titania, according to a titania solution producing method of the present invention
  • FIG. 3 is an explanatory diagram showing processes of producing a solution containing amorphous titania and anatase titania, according to a titania solution producing method of the present invention
  • FIG. 4 is a characteristic diagram showing an example carried out for confirming an effect of the present invention.
  • FIG. 5 is a characteristic diagram showing an example carried out for confirming an effect of the present invention.
  • FIG. 6 is a characteristic diagram showing an example carried out for confirming an effect of the present invention.
  • FIG. 7 is a characteristic diagram showing an example carried out for confirming the effect of the present invention.
  • FIG. 8 is a characteristic diagram showing examples carried out for confirming the effect of the present invention.
  • FIG. 9 is a characteristic diagram showing examples carried out for confirming the effect of the present invention.
  • FIG. 10 is a characteristic diagram showing examples carried out for confirming the effect of the present invention.
  • TIP titanium tetraalkoxide
  • IPA isopropanol
  • step S 3 the fine particles of titania are separated from the mother liquid by the use of, for example, a filter, then are subjected to airing to be dried at a predetermined temperature such as at 100° C. for 20 hours, for example, to thereby obtain powder (fine particle groups) of titania.
  • an acid solution such as a hydrogen peroxide solution, e.g. an aqueous solution containing 10 to 50 weight % of hydrogen peroxide (aqueous hydrogen peroxide)
  • a hydrogen peroxide solution e.g. an aqueous solution containing 10 to 50 weight % of hydrogen peroxide (aqueous hydrogen peroxide)
  • a temperature thereof at 20° C. or below, preferably at 5 to 20° C., to thereby dissolve a predetermined amount of the titania powder
  • titania is gelled so that a titania gel is produced.
  • This titania gel is composed of amorphous titania having no particle boundary.
  • the solution is agitated and simultaneously added with, as a dispersing agent, an acid solution such as a hydrogen peroxide solution, e.g. an aqueous solution containing 10 to 50 weight % of hydrogen peroxide (aqueous hydrogen peroxide), while a temperature of the solution is controlled at 20° C. or below, preferably at 5 to 20° C., so that the titania gel is transformed to a titania sol, i.e. formed into ultrafine particles, to be highly dispersed in the solution, thereby obtaining the solution containing amorphous titania and having a pH of, for example, about 1.
  • an acid solution such as a hydrogen peroxide solution, e.g. an aqueous solution containing 10 to 50 weight % of hydrogen peroxide (aqueous hydrogen peroxide)
  • a temperature of the solution is controlled at 20° C. or below, preferably at 5 to 20° C.
  • step S 6 a predetermined amount of an alkali solution such as ammonia, sodium hydroxide, or amin is added for decomposition so that a pH of the solution becomes, for example, 2 to 10, preferably 4 to 8.
  • the pH value is determined based on a kind of base material when the solution is used as a material of a coating film, particularly based on an acid-proof property or an alkali-proof property of the base material. In this manner, there is obtained the solution containing amorphous titania having the average particle size of, for example, 10 to 28 nm.
  • ammonia may be, for example, aqueous ammonia (ammonia aqueous solution).
  • the foregoing solution containing amorphous titania is, for example, used as a material of a coating film.
  • the solution is applied to and/or impregnated into the surface of a base material such as ceramics, metal, glass, or building material so as to be formed as a liquid thin film on the surface of the base material.
  • calcination is carried out at a temperature allowed depending on a kind of the base material, such as at 500° C., so that amorphous titania is transformed to anatase titania to thereby form on the surface of the base material a fine titania coating film that exhibits photocatalytic activity.
  • the calcination temperature is not particularly limited.
  • the titania solution is not exclusively used as the material of the coating film, but may also be used as, for example, a material of toilet water.
  • the pH of the solution is adjusted to 2 to 10, preferably 4 to 8, by adding alkali such as ammonia, and therefore, titania is rarely gelled or aggregated in the obtained solution even on standing for a long time. That is, there can be obtained the solution containing amorphous titania, which can maintain the state where fine particles of titania are highly dispersed, over a long term.
  • the amount of addition of the alkali solution to set the pH of the solution to one of the values within the foregoing range depending on a property such as an acid-proof property or an alkali-proof property of a base material
  • the solution suitable for such a base material can be prepared.
  • the pH of the solution may be set to, for example, around seven for suppressing corrosion of the surface of metal.
  • aqueous hydrogen peroxide is added while controlling the temperature of the solution at the predetermined temperature such as at 20° C. or below, preferably at 5 to 20° C. because titania becomes reluctant to be dissolved due to lowering of solubility if the temperature is too low.
  • the predetermined temperature such as at 20° C. or below, preferably at 5 to 20° C. because titania becomes reluctant to be dissolved due to lowering of solubility if the temperature is too low.
  • this makes it possible to control the dissolution rate of titania and prepare the solution in a relatively short time.
  • the calorific value caused by the heat of dissolution can be controlled, it is easy to control the temperature of the solution upon the preparation and it is possible to prepare the solution in a relatively short time.
  • step S 5 also in the process of transforming the titania gel to the titania sol (corresponding to step S 5 ), which is the secondary process, an effect like the foregoing can be achieved by adding aqueous hydrogen peroxide while controlling the temperature of the solution at the predetermined temperature such as at 20° C. or below, preferably at 5 to 20° C.
  • step S 7 in FIG. 2 there is prepared a solution containing amorphous titania and having a pH adjusted to, for example, 2 to 10, preferably 4 to 8, by adding the alkali solution in step S 6 in FIG. 1 .
  • step S 8 the solution is heated, while being agitated, by the use of heating means such as a water bath or an autoclave at a predetermined temperature such as at 60° C. or above, preferably at 95 to 120° C., for a predetermined time such as 1 to 12 hours.
  • amorphous titania is transformed to anatase titania to thereby obtain a solution containing fine particles of anatase titania.
  • a portion of the transformed titania becomes anatase-rutile type titania (anatase-rutile titania) that forms a mixture of anatase titania and rutile titania.
  • the solution containing anatase titania is applied to and/or impregnated into the surface of a base material such as ceramics, glass, metal, building material, resin or fiber so as to be formed as a coating thin film on the surface of the base material.
  • a base material such as ceramics, glass, metal, building material, resin or fiber
  • the solution containing anatase titania is used in this manner, calcination requiring high temperature heating is not necessary, and therefore, it is also applicable to coating of a base material such as resin that has a poor heat-proof property, and further applicable to coating of a base material such as an outside building that is difficult to calcine. From this aspect, the solution containing anatase titania is advantageously used.
  • the titania solution is not exclusively used as the material of the coating film, but may also be used as, for example, a material of toilet water.
  • the solution containing amorphous titania which has the pH of 2 to 10, preferably 4 to 8, it is possible to suppress gelling or aggregation of amorphous titania before the transformation in the heat treatment, particularly in the initial stage of the heat treatment. Consequently, there can be obtained the titania solution in which fine particles of anatase titania are highly dispersed. Further, in this case, inasmuch as it is possible to omit processes of decomposing excessive hydrogen peroxide contained in the solution and removing bubbles generated from hydrogen peroxide, it is advantageous in that the production efficiency can be improved. Incidentally, if the pH of the solution is higher than eight, the promotion of generation of titania nuclei is lowered.
  • titania is gelled in the heating, particularly in the initial stage of the heating as described above. That is, it is preferable to use the solution containing amorphous titania, which has a pH of 4 to 8.
  • titania dissolved in aqueous hydrogen peroxide for obtaining the amorphous titania gel is not limited to titania obtained using titanium tetraalkoxide as a material. It is also possible to use a solution containing a titanium hydroxide gel obtained using, as a material, an inorganic titanium compound such as titanium chloride or titanium sulfate. However, in this case, it is difficult to fully remove chlorine components or sulfuric acid components even by washing or calcination. If the chlorine or sulfuric acid components remain in the coating film, they are reacted with metal ions such as iron ions floating in the atmosphere to exhibit a light brown.
  • a coating film is formed on a base material such as an external wall, the surface thereof may look dirty although dirt proofing by virtue of photocatalytic reaction of titania is one of objects of forming the coating film on the base material. Accordingly, by using the organic material such as TIP like in this preferred embodiment, it is expected to prevent the coating film from coloring.
  • a method of producing a solution containing anatase titania using amorphous titania as a material will be described according to another preferred embodiment of the present invention.
  • the amorphous titania powder obtained in step S 3 in FIG. 1 for example, is added into water such as pure water, then agitated.
  • An ultrasonic treatment is applied to this solution, wherein, for example, ultrasonic waves are applied to the solution for a predetermined time, so that amorphous titania is formed into ultrafine particles which are highly dispersed in the water.
  • this water is heated to, for example, 100° C., so that amorphous titania is crystallized to be transformed to anatase to thereby obtain a solution in which ultrafine particles of anatase titania are highly dispersed.
  • this solution is mixed with the solution obtained in step S 7 in FIG. 2 , then the mixture is subjected to the heat treatment performed in step S 8 .
  • amorphous titania is pulverized into ultrafine particles and, when heated, these ultrafine particles serve as nuclei to promote generation of fine particles of anatase titania.
  • TIP titanium tetraalkoxide
  • IPA isopropanol
  • step S 12 by fully agitating the liquid mixture while controlling it at a predetermined temperature such as 25° C., hydrolysis of TIP is promoted so that fine particles of anatase titania being crystalline titania and fine particles of amorphous titania being non-crystalline titania are produced in the solution.
  • a predetermined temperature such as 25° C.
  • step S 11 TIP and IPA may be first mixed together, then IPA and the water may be mixed to this liquid mixture to achieve the foregoing predetermined mole ratio.
  • step S 13 the fine particles of anatase titania and amorphous titania are separated from the mother liquid by the use of, for example, a filter, then are subjected to airing to be dried at a predetermined temperature such as at 100° C. for 20 hours, for example, to thereby obtain powders (fine particle groups) of anatase titania and amorphous titania.
  • a predetermined temperature such as at 100° C. for 20 hours, for example, to thereby obtain powders (fine particle groups) of anatase titania and amorphous titania.
  • an acid solution such as a hydrogen peroxide solution, e.g.
  • an aqueous solution containing 10 to 50 weight % of hydrogen peroxide (aqueous hydrogen peroxide) is added to the titania powders and, by agitating the solution (titania dissolving liquid) while controlling a temperature thereof, for example, at 20° C. or below, preferably at 5 to 20° C., to thereby dissolve and disperse the titania powders in the solution.
  • a titania solution being a titania dispersed liquid in which fine particles of anatase titania and fine particles of amorphous titania are dispersed.
  • the foregoing titania solution is, for example, used as a material of a coating film.
  • the solution is applied to and/or impregnated into the surface of a base material such as ceramics, metal, glass, or building material so as to be formed as a liquid thin film on the surface of the base material.
  • a base material such as ceramics, metal, glass, or building material
  • a coating film is formed in which amorphous titania and anatase titania are uniformly dispersed.
  • the drying temperature is not particularly limited, but is preferably set to a temperature that does not promote formation of rutile titania.
  • anatase titania having a property of exhibiting photocatalytic activity is highly dispersed using amorphous titania as a binder. Therefore, the coating film has a high adhesion relative to the base material. Accordingly, it is possible to form the stable coating film with less exfoliation of titania.
  • the coating film may be heated to a high temperature such as 500° C. to transform amorphous titania to anatase titania.
  • the water is mixed so as to be excessive in amount relative to TIP, so that anatase titania being crystalline titania can be produced by the hydrolysis reaction of TIP. Therefore, anatase titania can be easily produced in a short time without carrying out the calcination or the high temperature heat treatment for a long time for the purpose of titania transformation which is required in the foregoing conventional technique. Consequently, it is possible to improve the productivity and reduce the production cost.
  • titania is produced by mixing the water so as to be excessive in amount relative to TIP, so that anatase titania being crystalline titania and amorphous titania being non-crystalline titania can be produced in one solution in the state where they are uniformly dispersed. Then, in the titania dispersed liquid wherein anatase titania and amorphous titania are dispersed in aqueous hydrogen peroxide, amorphous titania in the form of ultrafine particles serves to disperse particles of anatase titania, i.e.
  • amorphous titania is interposed among the particles of anatase titania, so that it is possible to suppress aggregation of the particles of anatase titania which is caused by mutual attraction thereof. Therefore, even if the titania dispersed liquid is left to stand over a long term, the state where anatase titania and amorphous titania are highly dispersed in the solution can be maintained so that the stability of the solution is high.
  • aqueous hydrogen peroxide when dissolving the titania powders in aqueous hydrogen peroxide, aqueous hydrogen peroxide is added while controlling the temperature of the solution at the predetermined temperature, for example, at 20° C. or below, preferably at 5 to 20° C. This makes it possible to control the dissolution rate of titania and prepare the solution in a relatively short time. As a result, it is possible to improve the productivity.
  • the foregoing preferred embodiment is not limited to the configuration wherein the water is mixed so as to be excessive in amount relative to TIP, but may also be configured that, for example, the water is mixed so as to be excessive in amount relative to TIP and IPA.
  • the production ratio of anatase titania can be increased by increasing the amount of the water, while the production ratio of amorphous titania can be increased by decreasing the amount of the water. That is, by controlling the mixing ratio of the materials being the condition of production reaction of titania, it is possible to easily produce a titania solution containing anatase titania and amorphous titania at desired concentrations.
  • an alkali solution such as ammonia, sodium hydroxide, or amin is added into the titania dispersed liquid obtained by dissolving titania in aqueous hydrogen peroxide in step S 14 in FIG. 3 , to thereby adjust a pH of the titania dispersed liquid to, for example, 2 to 10, preferably 4 to 8.
  • a pH of the titania dispersed liquid obtained by dissolving titania in aqueous hydrogen peroxide in step S 14 in FIG. 3 , to thereby adjust a pH of the titania dispersed liquid to, for example, 2 to 10, preferably 4 to 8.
  • a value thereof may be determined depending on, for example, a kind of base material.
  • a kind of base material For example, a kind of base material.
  • the pH of the solution is set to around seven for suppressing corrosion of the surface of the metal base material. With this configuration, it is possible to prepare the solution suitable for materiality of the base material such as an acid-proof property or an alkali-proof property, so that the surface of the base material is less corroded.
  • ammonia may be, for example, aqueous ammonia.
  • the titania solution being the titania dispersed liquid may contain alcohol such as IPA at a concentration of, for example, 50 weight % or less.
  • IPA may be added after dissolving the titania powders in aqueous hydrogen peroxide or, when the solution is used as the material of the coating film, IPA may be added before applying the solution onto the base material.
  • the solution contains IPA, aggregation of amorphous titania can be suppressed when, for example, the solution is applied to the surface of the base material. Consequently, the fine coating film can be formed.
  • the titania solution containing anatase titania and amorphous titania may be subjected to a heat treatment, such as a water-bath heat treatment, at 60° C. or above, preferably at 95 to 120° C., for a predetermined time such as 1 to 12 hours, to thereby transform amorphous titania to anatase titania to produce an anatase titania solution.
  • a portion of titania in the solution is transformed, by heating, to produce anatase-rutile type titania (anatase-rutile titania) that forms a mixture of anatase titania and rutile titania.
  • the weight ratio of this anatase-rutile titania be set to, for example, 4/6 (rutile/anatase), particularly 35/65.
  • the titania solution thus obtained exhibits extremely high activity under irradiation of ultraviolet light or visible light as obvious from the results of later-described examples.
  • the titania solution is not exclusively used as the material of the coating film, but may also be used as, for example, a material of toilet water.
  • titania solutions each particularly suitable as a material of a coating film.
  • the foregoing titania solution containing amorphous titania and/or anatase titania, and a solution containing silica such as amorphous silica being non-crystalline silica are mixed together to produce a titania solution containing silica.
  • the produced titania solution is applied to and/or impregnated into the surface of a base material and then dried to thereby form a coating film.
  • a solution as a liquid mixture of a precursor to amorphous silica such as TEOS (tetraethyl ortho silicate), and alcohol such as IPA (isopropyl alcohol) is added with an inorganic acid such as nitric acid to promote a hydrolysis reaction of TEOS, thereby producing fine particles of amorphous silica in the solution.
  • This solution containing amorphous silica is added with, for example, aqueous ammonia to adjust a pH, then the pH-adjusted solution is added into the titania solution obtained through the foregoing processes to produce a solution containing amorphous and/or anatase titania and amorphous silica.
  • the produced solution is added with aqueous ammonia to adjust a pH, then the pH-adjusted solution is applied to and/or impregnated into the surface of a base material and dried, thereby forming a titania-silica coating film.
  • the coating film thus formed has silica existing therein, the refractive index of light on the surface thereof is lowered. Therefore, it is possible to suppress reflection of light such as sunlight or illumination light on the surface thereof as compared with the coating film containing only titania. Further, the reflection state of light can be controlled by adjusting the content of silica.
  • two or more coating films may be stacked on the surface of a base material. Specifically, after forming a coating film on the surface of the base material, another coating film is formed on the surface of such a coating film by the use of the same technique. In this case, films of different kinds may be stacked, e.g.
  • a titania-silica film may be formed on a titania film, or films of the same kind may be stacked, e.g. titania films or titania-silica films may be stacked.
  • the number of film layers may be determined depending on, for example, a kind of base material.
  • a solution containing silica is not limited to a solution containing amorphous silica, but may be a solution wherein, for example, particle groups of crystalline silica are dispersed.
  • a solution containing amorphous titania was produced using the foregoing technique.
  • the liquid mixture was agitated while controlling a temperature thereof at 25° C., to thereby produce fine particles of titania.
  • Titania was separated from the mother liquid through suction filtration, then dried by airing at 100° C. to thereby obtain titania powder.
  • the titania powder was added with 31 weight % aqueous hydrogen peroxide, then this solution was agitated while being controlled at 10° C., to thereby obtain a titania gel. After further adding 31 weight % aqueous hydrogen peroxide, ammonia was added into the solution to adjust a pH to 7. The thus obtained solution containing fine particles of amorphous titania was left to stand at normal temperature, and the state of the solution after a lapse of one week, particularly whether or not titania was gelled or aggregated, was confirmed.
  • This comparative example was the same as Example 1 except that the alkali solution was not added.
  • a pH of a solution obtained in this comparative example was 1.
  • Example 1 Comparative Example 1
  • Comparative Example 2 The result of comparison among Example 1, Comparative Example 1, and Comparative Example 2 is shown in FIG. 4 .
  • the solution of Comparative Example 1 was increased in viscosity after several days, then titania was gelled after a lapse of one week, and the solution exhibited a yellow.
  • titania was not gelled or aggregated even after a lapse of one week.
  • the solution of Comparative Example 2 was not subjected to gelling or aggregation of titania.
  • several days were required for decomposing excessive hydrogen peroxide while producing the solution, and therefore, it is not practical in terms of the production efficiency. From the foregoing result, it has been confirmed that gelling and aggregation of titania can be suppressed by adding ammonia.
  • titania powder was dissolved in aqueous hydrogen peroxide while controlling the solution at a predetermined temperature.
  • This process corresponds to step S 4 in FIG. 1 .
  • 1 g of amorphous titania powder was measured into each of 100 ml sample bottles, and 15 weight % aqueous hydrogen peroxide was added thereto.
  • thermostats were used to control temperatures of the solutions at 5° C., 10° C., 20° C., 30° C., and 40° C., respectively.
  • a time dissolution time
  • the result about a dissolution time at each temperature was shown in FIG. 5 .
  • the dissolution time was 82 minutes at 5° C., 51 minutes at 10° C., and 20 minutes at 20° C.
  • the dissolution time was 15 minutes at 30° C. and 40° C., respectively, wherein the dissolution time was substantially constant at 30° C. or higher. From the foregoing result, it has been confirmed that the dissolution rate of titania differs depending on the temperature of the solution, and it is possible to control the dissolution rate of titania, i.e. the calorific value caused by the heat of dissolution, by controlling the temperature of the solution.
  • a titania dispersed liquid was produced using the foregoing technique of mixing water excessive in amount relative to TIP.
  • the liquid mixture was agitated while being controlled at 25° C., to thereby produce fine particles of titania.
  • Titania was separated from the mother liquid through suction filtration, then dried by airing at 100° C. to thereby obtain titania powder.
  • the titania powder was added with 31 weight % aqueous hydrogen peroxide, then this solution was agitated while being controlled at 20° C., to thereby obtain a titania dispersed liquid. This dispersed liquid is called a solution A.
  • Powder X-ray diffraction was carried out for analyzing crystal systems of the titania particles contained in the solution A and the solution D obtained in Example 3 and Comparative Example 3, respectively. First, the solutions were dried at 120° C. for one hour to obtain sample powders for measurement, respectively. Then, these samples were analyzed by the use of a powder X-ray diffractometer.
  • the diffraction result about titania in the solution A is shown in FIG. 6
  • the diffraction result about titania in the solution D is shown in FIG. 7 .
  • a peak P 1 of amorphous titania and a peak P 2 of anatase titania appear in the diffraction spectrum of titania in the solution A
  • only a peak P 1 of amorphous titania appears in the diffraction spectrum of titania in the solution D.
  • both amorphous titania and anatase titania can be produced by mixing the water excessive in amount relative to TIP.
  • titania dispersed liquid was produced using the solution A of Example 3.
  • Aqueous ammonia was added to the solution A produced as described above to adjust a pH of the solution to 3 to 4, then this solution was subjected to a water-bath heat treatment at 97° C. for 4 hours.
  • This titania dispersed liquid is called a solution B.
  • a titania dispersed liquid was produced like in Example 4 except that a water-bath heat treatment was carried out at 97° C. for 9 hours.
  • This dispersed liquid is called a solution C.
  • a solution containing anatase titania was produced based on the technique described in detail in Patent Literature 3 referred to in the column of “BACKGROUND OF THE INVENTION”.
  • a 60 weight % titanium tetrachloride aqueous solution and 2.5 weight % aqueous ammonia were mixed together to produce titanium hydroxide.
  • 30 weight % aqueous hydrogen peroxide was added to thereby obtain a titanic acid solution.
  • Non-reacted hydrogen peroxide was decomposed on standing.
  • an anatase titania dispersed liquid was obtained. This solution is called a solution F.
  • each of the solutions A to C in Examples 3 to 5 and the solutions D to G in Comparative Examples 3 to 6 was measure into 3 ml of distilled water containing a fluorescent reagent (concentration of HPF (hydroxyphenyl fluorescein) was 10 ⁇ M) to thereby produce samples for analysis. That is, each of the solutions A to G was diluted to 1 volume %. Each sample was placed under irradiation of ultraviolet light by the use of a blacklight for 10 minutes while being agitated. Thereafter, the irradiation of ultraviolet light was stopped and each sample was agitated for 10 minutes in darkness.
  • a fluorescent reagent concentration of HPF (hydroxyphenyl fluorescein) was 10 ⁇ M
  • This test was the same as Test 2 except that visible light was irradiated using a fluorescent lamp in place of the irradiation of ultraviolet light using the blacklight. The result is also shown in FIG. 8 .
  • the radical production rates were 248 (nM/s) under irradiation of ultraviolet light and 41 (nM/s) under irradiation of visible light, which were much smaller than those in Examples 4 and 5 (solutions B and C).
  • the solution G containing oxygen deficient titania and the amorphous titania solution D radicals were hardly produced under irradiation of visible light.
  • the solution E obtained by applying the water-bath heat treatment to the solution D the results were approximately the same as those of the solution D both under irradiation of ultraviolet light and under irradiation of visible light.
  • the diffraction result corresponding to prescribed wavelengths is extracted and shown in FIG. 9 .
  • the present inventors have confirmed that a peak P 3 appearing in a region over a range of about 22 to 30[°] is a peak that is formed by a peak P 4 of anatase titania and a peak P 5 of rutile titania conjointly at a certain ratio. Note that, with respect to the peaks P 4 and P 5 , a peak of anatase titania alone and a peak of rutile titania alone obtained in advance by performing X-ray diffraction are shown in a superimposed fashion.
  • anatase-rutile type titania is produced in the solution, which is in the form of a mixture of anatase titania and rutile titania each having an extremely small particle size of about 2.7 nm and has a weight ratio of about 4/6 (rutile/anatase). It is presumed that the inclusion of such anatase-rutile type titania in the solution enables the exhibition of high activity not only under irradiation of ultraviolet light but also under irradiation of visible light.
  • an amorphous titania dispersed liquid was produced using the foregoing technique (steps S 1 to S 6 in FIG. 1 ), and was further subjected to a water-bath heat treatment.
  • Titania produced in this liquid mixture was separated and then dried by airing at 100° C. to thereby obtain titania powder.
  • the titania powder was added with 31 weight % aqueous hydrogen peroxide, then this solution was agitated while being controlled at 10° C. After further adding 31 weight % aqueous hydrogen peroxide, ammonia was added into the solution to adjust a pH to 3 to 4. Then, the solution was subjected to a water-bath heat treatment at 97° C. for 9 hours.
  • This titania dispersed liquid is called a solution H.
  • This example is the same as Example 6 except that a water-bath heat treatment was carried out at 97° C. for 5 hours.
  • This titania dispersed liquid is called a solution I.
  • This example is the same as Example 6 except that a water-bath heat treatment was carried out at 97° C. for 20 hours.
  • This titania dispersed liquid is called a solution J.
  • This test was the same as Test 4 except that visible light was irradiated using a fluorescent lamp in place of the irradiation of ultraviolet light using the blacklight. The result is also shown in FIG. 10 .
  • the solutions B and C of Examples 4 and 5 exhibit higher activity as compared with the solutions H to J of Examples 6 to 8. That is, it is understood that the solution containing amorphous titania and anatase titania, which is obtained by mixing the water in an excessive amount relative to TIP, is suitable for producing more securely anatase-rutile type titania that exhibits high activity.

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US20090163647A1 (en) * 2007-12-21 2009-06-25 Envont Llc Hybrid metal oxides
US20090162560A1 (en) * 2007-12-21 2009-06-25 Envont L.L.C. Hybrid vehicle systems
US20090163656A1 (en) * 2007-12-21 2009-06-25 Envont Llc Hybrid vehicle systems
US20110089018A1 (en) * 2009-10-19 2011-04-21 Industrial Technology Research Institute Method for one step synthesizing and immobilizing crystalline TiO2 nano-particles simultaneously on polymer support and use of the same
KR101082058B1 (ko) 2009-02-18 2011-11-10 한국수력원자력 주식회사 나노크기의 이산화티타늄 제조방법 및 이를 이용한 원자로 증기발생기 전열관의 응력부식균열 억제방법
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US20130153406A1 (en) * 2011-12-14 2013-06-20 Electronics And Telecommunications Research Institute Methods of manufacturing metal oxide nanoparticles

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